Change irc.freenode.net to chat.freenode.net

On the [freenode website][1], it says that the main server is `chat.freenode.net`.

> Our main server rotation is `chat.freenode.net`. Pointers to freenode currently include irc.ghostscript.com, 
> irc.gnu.org, irc.handhelds.org, and irc.kde.org. 

This seems to be their recommended URL for connecting, and so I have changed the code to point towards that (I have left the `test/irc_test.js`, which came up when I ran `grep -r irc\.freenode\.net *`, as `irc.freenode.net`, as that seems like an internal script which can be easily fixed.

[1]: http://freenode.net/irc_servers.shtml